Medical particle irradiation apparatus

ABSTRACT

Disclosed is a medical particle irradiation apparatus comprising a rotating gantry  1  including an irradiation unit  4  emitting particle beams; an annular frame  16  located within and supported by the rotating gantry  1  such that it can rotate relative to the rotating gantry  1 ; an annular frame  15  fixedly located opposite the annular frame  16 ; an anti-corotation mechanism  34  being in contact with both the annular frames  16  and  15  to prevent the annular frame  16  from rotating together with the rotating gantry  1  during rotation of the rotating gantry  1 ; and a flexible moving floor  17  interposed between the annular frames  15  and  16 , the flexible moving floor  17  being engaged with the annular frames  15  and  16  in such a manner as to move freely such that its bottom is substantially level and that it moves as the rotating gantry rotates.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a medical particleirradiation apparatus, and more particularly to a medical particleirradiation apparatus which is suitable for rotating around the patientand irradiating the patient with particle beams from a desired locationin the circumferential direction.

2. Description of the Related Art

Particle beams (e.g., proton beam) have captured the spotlight in recentyears in radiation therapy (treatment) for cancer as they can treatcancer with relatively small damage to normal cells.

An example of rotary irradiation room for radiation therapy usingparticle beams is described in Patent Document 1. This rotaryirradiation room for radiation therapy has a semicylindrical path with alevel bottom formed at each of the fixed and mobile ring rails which areprovided opposite each other with the radiation irradiation unit betweenthem, and the flexible moving floor provided within this path is movedin synchronization with the rotation of the radiation irradiation unit.Further, the drive motor provided on the rotating gantry rotates themobile ring rail in the direction opposite to the radiation irradiationunit's rotation direction by the same amount as the amount of rotationof the radiation irradiation unit. This keeps the positionalrelationship between the fixed and mobile ring rails which are locatedopposite each other and allows consistent formation of a level floorused for access to the therapy bed and the radiation irradiation uniteven when the rotating gantry rotates.

However, this prior art requires a drive motor for rotating the mobilering rail in the direction opposite to the rotating gantry's rotationdirection and a tilt sensor for detecting the relative positionalrelationship between the semicylindrical passages formed at the fixedand mobile ring rails and moreover a control unit for controlling them,thus making the configuration complex.

Therefore, an example of rotary irradiation room for particle beamtherapy addressing this problem is described in Patent Document 2. Thisrotary irradiation room for particle beam therapy comprises a fixedshell and fixed shell-side guide rail and rotary shell-side guide railand activates the locking rod using motor-operated cylinders provided onthe fixed shell; this locking rod is engaged with an engagement holesprovided on the rotary shell-side guide rail during rotation of therotating gantry. For this reason, the rotation of the rotary shell-sideguide rail is inhibited by the locking rod during rotation of therotating gantry, thus making it possible to keep the positionalrelationship between the fixed and rotary shell-side guide rails whichare located opposite to each other and keep the bottom of the movingfloor constantly level. Two motor-operated cylinders and two engagementholes are provided; the locking rod is pulled out of the engagement holeand reduced in size on the side where the rotation of the particleirradiation unit is hindered while the locking rod is kept in theengagement hole on the side where the rotation is not hindered.

[Patent Document 1]

Japanese Patent Application Laid-open (kokai) Publication No.Hei11-47287

[Patent Document 2]

Japanese Patent Application Laid-open (kokai) Publication No.2001-129103

Although the drive motor and the tilt sensor in the prior art describedin Patent Document 1 are not needed, the prior art described in PatentDocument 2 additionally requires locking rods, motor-operated cylindersand a control unit for causing the locking rod to extend or retract withrotation of the particle irradiation unit and attaching and detachingthe locking rod, thus resulting in insufficient simplification of theconfigurations.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to provide a medicalparticle irradiation apparatus which ensures more simplified structureand allows formation of the substantially level access floor regardlessof the position of the irradiation unit which emits particle beams.

The above object can be achieved by providing an anti-corotation unitwhich is in contact with both a first frame located within and supportedby a rotating gantry such that it can rotate relative to the rotatinggantry and a second frame fixedly located opposite the first frame andwhich prevents the first frame from rotating together with the rotatinggantry during rotation of the rotating gantry. Further, the flexiblemoving floor, interposed between the first and second frames, is engagedwith the first and second frames in such a manner as to move freely suchthat its bottom is substantially level, that it forms therein a particleirradiation room into which a therapy bed is slid and that it moves asthe rotating gantry rotates.

Since the anti-corotation unit is in contact with the first frame,located within the rotating gantry such that it can rotate relative tothe rotating gantry, and the fixed second frame, the anti-corotationunit which is in contact with the second frame can prevent rotation ofthe first frame even if the first frame attempts to rotate together withthe rotating gantry during rotation of the rotating gantry. Therefore,the positions of the first and second frames which are located oppositeeach other can be kept substantially unchanged even if the rotatinggantry rotates. Consequently, it is possible for the flexible movingfloor to form a substantially level access floor regardless of theposition of the irradiation unit emitting particle beams.

Moreover, since the anti-corotation unit is located on the rotatinggantry, it is moved in the rotating gantry's rotation direction as aresult of rotation of the rotating gantry. However, the presentinvention eliminates the need for the drive motor described in PatentDocument 1 which rotates the mobile ring rail in the direction oppositeto the rotation direction of the radiation irradiation unit by the sameamount as the amount of rotation of the radiation irradiation unit andthe drive unit exclusively for the anti-corotation unit, an equivalentof the motor-operated cylinder described in Patent Document 2 whichmoves the locking rod. The present invention does not require anyexclusive drive unit for the anti-corotation unit and any control unitfor this drive unit, thus allowing simplification of the structure.

It is also possible to dispose the anti-corotation unit on theirradiation unit which rotates together with the rotating gantry duringrotation of the rotating gantry and emits particle beams. Disposition ofthe anti-corotation unit on the irradiation unit means that theanti-corotation unit lies on the rotating gantry although it is notdirectly disposed on the rotating gantry.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, aspects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 illustrates the schematic configuration of a medical particleirradiation apparatus which is a preferred embodiment of the presentinvention;

FIG. 2 is a perspective view of a rotating gantry employed in themedical particle irradiation apparatus of FIG. 1;

FIG. 3 is a transverse sectional view, showing the sectional structureof an irradiation room for particle beam therapy disposed in therotating gantry of FIG. 2, FIG. 3 being a sectional view taken alongline IV—IV of FIG. 5;

FIG. 4 is a conceptual longitudinal sectional view showing the overallschematic structure of the irradiation room for particle beam therapydisposed in the rotating gantry shown in FIG. 2;

FIG. 5 is a longitudinal sectional view showing the detailed structureof major portions of the irradiation room for particle beam therapyshown in FIG. 4;

FIG. 6 is a sectional view taken along line V—V of FIG. 4;

FIG. 7 is an enlarged sectional view of portion A of FIG. 5, showing thesupport structure at both ends of a moving floor;

FIGS. 8A and 8B illustrate the structure of a conveyor chain shown inFIG. 7, with FIGS. 8A and 8B being a top plan view and a side view,respectively, of the conveyor chain;

FIG. 9 is a longitudinal sectional view showing the detailed structureof major portions of the irradiation room for particle beam therapyemployed in the medical particle irradiation apparatus which is anotherembodiment of the present invention;

FIG. 10 is a transverse sectional view of the irradiation room forparticle beam therapy of FIG. 9;

FIG. 11 is an enlarged sectional view of portion A′ of FIG. 9, showingthe support structure at both ends of an anti-corotation mechanism; and

FIG. 12 is an enlarged sectional view of portion B′ of FIG. 9, showingthe support structure at both ends of the moving floor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of the present invention will now be described withreference to the drawings.

A medical particle irradiation apparatus of this embodiment is describedreferring to FIGS. 1 and 2. The medical particle irradiation apparatusof this embodiment is designated at 40 and comprises a charged particlebeam generating unit 41 and a rotating gantry 1. The charged particlebeam generating unit (particle beam generating unit) 41 has an ionsource not shown, a preaccelerator 42 and a synchrotron 43. Ionsgenerated in the ion source (e.g., proton ions (or carbon ions)) areaccelerated by the preaccelerator 42 (e.g., linear accelerator). The ionbeam emitted by the preaccelerator 42 enters the synchrotron 43. Thatbeam which is a charged particle beam (particle beam) is accelerated inthe synchrotron 43 as it is given energy by radio-frequency powerapplied by a radio frequency accelerating cavity 44. After the energy ofthe ion beam orbiting within the synchrotron 43 is raised to the presetenergy (normally 100 to 200 MeV), radio frequency is applied to the ionbeam by a radio frequency application unit for emission 45. The ion beamorbiting within the stability limit moves outside the stability limit asa result of this radio frequency application, passes through an emissiondeflector 50 and is emitted from the synchrotron 43. At the time of ionbeam emission, currents introduced into electromagnets such as aquadrupole electromagnet 46 and a polarized electromagnet 47 are kept atthe preset value, with the stability limit kept nearly constant.Stopping the radio frequency application unit 45 from applying radiofrequency allows ion beam emission from the synchrotron 43 to bestopped.

The ion beam emitted by the synchrotron 43 reaches a particleirradiation unit (irradiation nozzle) 4 via a beam transfer system 49.The affected area (cancer-affected area) of a patient 8 on a therapy bed59 is irradiated with the ion beam from the particle irradiation unit 4.The particle irradiation unit 4 generates ion beam which forms anoptimal dose distribution for particle beam therapy.

The rotating gantry 1 comprises a rotary shell (rotational element) 3 insubstantially cylindrical form having a front ring 2 and a motor(rotation unit) not shown for rotating the rotary shell 3. The frontring 2 provided at one end of the rotary shell 3 is supported by aplurality of rotatable support rollers 6. These support rollers 6 areattached to a support unit 10, which is disposed in a rotating gantrydisposition area (building foundation) 9, such that they are free torotate as shown in FIG. 3. Although not shown, the other ring (whoseouter diameter is equal to that of the front ring 2) provided at theother end of the rotary shell 3 is supported by a plurality of thesupport rollers 6 attached to the other support unit 10 such that theyare free to rotate. A reverse U-shaped beam transfer unit 5, which ispart of the beam transfer system 49, and the particle irradiation unit 4are provided on the rotary shell 3 and rotate as the rotating gantry 1rotates. The beam transfer unit 5 has electromagnets such as polarizedelectromagnets 51 and 52. A therapy gauge (therapy room) 14 is formedwithin the rotary shell 3.

The medical particle irradiation apparatus 40 has an irradiation roomfor particle beam therapy 55 provided within the rotary shell 3 of therotating gantry 1. The detailed structure of the irradiation room forparticle beam therapy 55 is described by referring to FIGS. 4 and 5. Theirradiation room for particle beam therapy 55 comprises a fixed annularframe (ring member) 15, an annular frame 16, a moving floor 17 and ananti-corotation mechanism (frame position retaining unit, positionretaining unit) 34.

The annular frame 15 is provided on the front ring 2 side of the rotaryshell 3 and secured to a base 18 disposed in the rotating gantrydisposition area 9. The annular frame 16 is provided on the other sideof the rotary shell 3 and located across a path of the particleirradiation unit 4 from the annular frame 15. The annular frame 16 issupported by a plurality of support rollers 20 attached to a supportframe 19, which is secured to the inner surface of the rotary shell 3,such that they are free to rotate. That is, the annular frame 16 is freeto rotate relative to the rotating gantry by the support rollers 20. Theannular frames 15 and 16 comprise on their respective opposed sides ringguide portions 15A and 16A in which guide grooves with level bottom andcircular top are formed. The guide grooves are semicylindrical in shapeas a result of their level and circular portions.

The moving floor 17, as shown in FIG. 6, has a flexible structure with anumber of plates 24 in which the adjacent plates 24 are connected toeach other with links not shown. Each of the plates 24 is arranged suchthat it faces the center of rotation of the rotating gantry 1. Themoving floor 17 possesses sufficient stiffness to defy deformation evenwhen a doctor or others 13 works on top of it. One end of the movingfloor 17 is engaged with the guide groove of the ring guide portion 15Awhile the other end with the guide groove of the ring guide portion 16A.The structure of that engagement condition is described using FIG. 7.Each of the plates 24 is slightly shorter than the distance between theopposed sides of the ring guide portions 15A and 16A. A wheel 25 isattached to each end of the plates 24. Each of the wheels 25 located atthe end on the annular frame 16 side of each of the plates 24 is slidinto a guide groove 56 formed on the ring guide portion 16A. Althoughnot shown, each of the wheels 25 located at the end on the annular frame15 side of each of the plates 24 is slid into the guide groove 56 formedon the ring guide portion 15A. Further, a side wheel 26 which rotateswhile being in contact with the side of the ring guide portion 16A isprovided at the end on the annular frame 16 side of each of the plates24. Although not shown, the side wheel 26 which rotates while being incontact with the side of the ring guide portion 15A is provided at theend on the annular frame 15 side of each of the plates 24.

Moreover, each of the circumferential ends of the moving floor 17 iscoupled to the particle irradiation unit 4 via a telescopic cylinder 60and a pin 61, with the pin 61 attached to the particle irradiation unit4 to couple the cylinder 60 so as to allow its free rotational movement.Additionally, the pin 61 is also supported by the rotary shell 3 via asupport base member 62. This makes it possible to control thecircumferential position of the moving floor 17 through extension orretraction (OUT/IN of the rod portion) of the cylinder 60.

If the rotating gantry 1 rotates as it is driven by a motor, theparticle irradiation unit 4 moves in that rotation direction. The movingfloor 17 which is coupled to the particle irradiation unit 4 by the pin61 and the cylinder 60 also moves in that rotation direction as it ispulled by the cylinder 60 coupled to the particle irradiation unit 4.Movement of the moving floor 17 is carried out smoothly along therespective guide grooves 56 of the ring guide portions 15A and 16A sincethe wheels 25 are provided for each of the plates 24. Movement of themoving floor 17 along the circular portion and from the level tocircular portions (or from the circular to level portions) of each ofthe guide grooves 56 is also carried out smoothly since the moving floor17 couples the adjacent plates 24 with links not shown so as to beflexible.

The moving floor 17, engaged with the ring guide portions 15A and 16A,forms a level floor portion 57 at the bottom of the annular frames 15and 16 by the level portion of each of the guide grooves 56 and acircular wall portion 58 at the top of the annular frames 15 and 16 bythe circular portion of each of the guide grooves 56. The therapy gauge14 is formed inside the moving floor 17. The therapy bed 59 is slid intothe therapy gauge 14 when ion beam is emitted from the particleirradiation unit 4. A therapy stage 7 equipped with the therapy bed isdisposed on top of a therapy stage disposition area 11 which is one stephigher than the rotating gantry disposition area 9, as shown in FIG. 4.The therapy stage 7 is attached. The therapy stage 7 further comprises adrive unit (bed drive means) 12. The therapy bed 59 is moved by thedrive unit (bed drive means) 12 and slid into and out of the therapygauge 14. When the therapy bed 59 is in the therapy gauge 14, theposition of the therapy bed 59 along its height is adjusted by the driveunit 12 such that the patient 8 on the therapy bed 59 or on the therapystage 7 is at a center of rotation k of the rotating gantry 1. Further,the therapy bed 59 is positioned by the drive unit 12 such that theaffected area (position to be irradiated with ion beam) of the patient 8is on the line extended from the axis of the particle irradiation unit4. This allows irradiation of the affected area of the patient 8 withion beam emitted from the particle irradiation unit 4. Since the movingfloor 17 is moved in the direction in which the particle irradiationunit 4 moves as a result of the rotation of the rotating gantry 1, it ispossible to irradiate the affected area of the patient 8 with ion beamfrom 360-degree range in the circumferential direction of the rotaryshell 3.

The floor level of the rotating gantry disposition area 9 is one steplower to secure a rotation radius of the rotating gantry 1. In contrast,the level of the therapy stage disposition area 11's top surface isnearly the same as that of the level floor portion 57's top surface inconsideration of access of the doctor 13 (or medical technologist,nurse) to the level floor portion 57. For this reason, a difference inheight ΔH (FIGS. 1 and 2) between the top surfaces of the rotatinggantry disposition area 9 and the therapy stage disposition area 11 isnormally 6 to 8 m. Since the level floor portion 57 is formed, it ispossible for the doctor or others 13 to readily and safely engage inmedical practice for the patient 8 on the therapy bed 59, which is slidinto the therapy gauge 14, at a height 6 to 8 m above the rotatinggantry disposition area 9 before and after ion beam irradiation byentering the therapy gauge 14.

The moving floor 17, engaged with the ring guide portions 15A and 16A,forms the level floor portion 57 which serves as scaffolding for thedoctor 13 (or medical technologist and so on) to work and forms thetherapy gauge 14 which provides a closed space from surrounding areas.Formation of the therapy gauge 14, which is a closed space, prevents thepatient 8 on the therapy bed 59 from having fear due to height.

The cylinder 60 attached to the moving floor 17 is a drive cylinderdisclosed in Japanese Patent Application Laid-open (kokai) PublicationNo. 2001-353228. The drive cylinder is controlled to extend or retractaccording to the rotation angle of the particle irradiation unit 4 (inother words, rotation angle of the rotating gantry 1). Therefore, themoving floor 17 is never short despite its reduction in size regardlessof the rotation angle by which the particle irradiation unit 4 moves,thus reliably securing the level floor portion 57 serving as scaffoldingnear the therapy bed 59.

The prime feature of this embodiment is provision of the anti-corotationmechanism 34 which rotates on its axis while being engaged (in contact)with the respective outer radius portions of the annular frames 15 and16 during rotation of the rotating gantry 1 and keeps the positions ofthe annular frames 15 and 16 positioned opposite each othersubstantially unchanged by revolving together with the rotating gantry1. The anti-corotation mechanism 34 has a connecting shaft (shaftmember) 36 attached to bearings 35 disposed on the inner surface of therotating gantry 1's rotary shell such that it is free to rotate (rotateon its axis) and sprockets 37 and 38 which are rotational elements, eachattached to one end of the connecting shaft 36, as shown in FIGS. 5 and7. The anti-corotation mechanism 34 is disposed at least at one location(preferably at several locations), for example, in the circumferentialdirection of the rotary shell 3. The anti-corotation mechanism 34 isdisposed in the circumferential direction of the rotary shell 3, at adistance from the particle irradiation unit 4 and on the inner surfaceof the rotary shell 3 such that it is rotatable.

Conveyor chains (endless links) 28 serving as uneven portions areattached to the outer radial surfaces of the ring guide portions 15A and16A. The detailed structure of the conveyor chains 28 is shown in FIGS.8A and 8B. Each of the conveyor chains 28 is formed into endlessconfiguration by arranging a number of link members 29 and link members59 alternately and connecting them with pins 30 through articulatedconnection such that they are free to move rotationally. Each of thelink members 29 is provided with a bracket portion 31 having a bolt hole32 on each side. The link members 29 are disposed on the outer radialsurface of the ring guide portion 16A by attaching fixing bolts 33,threaded through the bolt holes 32, to the outer radius portion of thering guide portion 16A. When all the link members 29 are disposed on theouter radial surface of the ring guide portion 16A, one of the conveyorchains 28 is disposed on the outer radial surface of the ring guideportion 16A as shown in FIG. 7. The other conveyor chain 28 is similarlydisposed on the outer radial surface of the ring guide portion 15A.

The sprocket 37 of the anti-corotation mechanism 34 meshes with theconveyor chain 28 disposed on the outer radial surface of the ring guideportion 15A. The other sprocket 38 of the anti-corotation mechanism 34meshes with the conveyor chain 28 disposed on the outer radial surfaceof the ring guide portion 16A. In other words, the sprocket 37 is incontact with the conveyor chain 28 disposed on the ring guide portion15A while the sprocket 38 with the conveyor chain 28 disposed on thering guide portion 16A.

The sprockets 37 and 38 both have the same numbers of teeth, with theirtooth pitches being equal. The conveyor chains 28 disposed respectivelyon the ring guide portions 15A and 16A both have the same numbers of thelink members 29 and 59, with the pin 30 pitches being equal. A center ofrotation m of the connecting shaft 36 (axis of the sprocket 37 or 38) isparallel with the center of rotation k of the rotating gantry 1 (=axisof the annular frame 15 or 16). In other words, the distance from theaxis of the sprocket 37 to the axis of the annular frame 15 is equal tothe distance from the axis of the sprocket 38 to the axis of the annularframe 16. This allows the anti-corotation mechanism 34 to function as aposition retaining unit which keeps the positions of the annular frames15 and 16, which are located opposite each other, substantiallyconstant.

In this embodiment, one of the conveyor chains 28 is indirectly attachedto the annular frame 15 via the ring guide portion 15A while the otherindirectly attached to the annular frame 16 via the ring guide portion16A. However, one of the conveyor chains 28 may be directly attached tothe outer radial surface of the annular frame 15 on which the guidegroove 56 is formed while the other conveyor chain 28 attached directlyto the outer radial surface of the annular frame 16 on which the guidegroove 56 is formed. Such indirect and direct attachment structures areboth none other than formation of mating portions on the annular frames15 and 16 which mesh with a pair of rotational elements provided on theanti-corotation mechanism 34.

Next, the operation and functions of this embodiment are described.

The rotating gantry 1 is allowed to rotate by driving a rotating gantrymotor. The rotating gantry 1 stops rotating when the ion beamirradiation direction, determined in the therapy program for the patient8, agrees with the axis of the particle irradiation unit 4. Then thetherapy bed 59, on which the patient 8 lies, is slid into the therapygauge 14 to perform positioning such that the affected area of thepatient 8 is on the line extended from the axis of the particleirradiation unit 4.

When the rotating gantry 1 rotates, the rotary shell 3 rotates. Sincethe annular frame 16 is held via the support rollers 20 such that it isfree to rotate, the annular frame 16 also attempts to rotate withrotation of the rotary shell 3 as a result of friction and so ongenerated by the support rollers 20 and so on. This phenomenon isreferred to as corotation. Note that since the moving floor 17 alsomoves within the guide groove 56 of the ring guide portion 16A as aresult of movement of the particle irradiation unit 4 associated withrotation of the rotary shell 3, corotation of the annular frame 16 mayfurther intensify due to contact friction and so on of the moving floor17 which moves. However, corotation does not take place with the annularframe 15 since it is secured to the base 18.

Since the anti-corotation mechanism 34 is provided in this embodiment,the annular frame 16 is prevented from rotating together with therotating gantry when the rotating gantry 1 rotates. The reason for thisis described below.

The anti-corotation mechanism 34 is attached to the rotary shell 3 viathe bearings 35, and since the sprockets 37 and 38 mesh with theconveyor chains 28 disposed respectively on the ring guide portions 15Aand 16A, the anti-corotation mechanism 34 moves in the rotationdirection of the rotary shell 3 (movement direction of the particleirradiation unit 4) while rotating on its axis as the rotary shell 3rotates. Movement of the anti-corotation mechanism 34 in the rotationdirection of the rotary shell 3 (movement direction of the particleirradiation unit 4) is revolution of the anti-corotation mechanism 34along the outer radius portions of the ring guide portions 15A and 16A.

Since the sprocket 37 meshes with the conveyor chain 28 provided on thefixed ring guide portion 15A, the sprocket 38 which is secured to thesprocket 37 by the connecting shaft 36 prevents the ring guide portion16A, that is, the annular frame 16 from rotating during revolution ofthe anti-corotation mechanism 34 by mating with the conveyor chain 28provided on the ring guide portion 16A. The capability of theanti-corotation mechanism 34 to prevent the annular frame 16 fromrotating is activated throughout revolution of the anti-corotationmechanism 34. Therefore, the annular frame 16 does not rotate and alwaysstands still even when the rotating gantry 1 rotates. In thisembodiment, the positions of the annular frames 15 and 16 locatedopposite each other remain substantially unchanged even when the rotaryshell 3, that is, the rotating gantry 1 rotates. Although rotation ofthe rotating gantry 1 results in movement of the moving floor 17 alongthe guide grooves 56 of the ring guide portions 15A and 16A, the levelfloor portion 57 is kept substantially level at all times below theannular frames 15 and 16 in this embodiment since the positions of theannular frames 15 and 16 located opposite each other remainsubstantially unchanged.

This makes it possible to secure work space for safe engagement inmedical practice by the doctor 13 or others by the level floor portion57 formed near the therapy bed 59 which is slid into the therapy gauge14.

As mentioned earlier, since the annular frame 16 is attached to therotary shell 3 by the support rollers 6 such that it can rotate relativeto the rotary shell 3, the rotary shell 3, that is, the rotating gantry1 can rotate around the annular frame 16 even if the annular frame 16substantially always stands still.

If the above-mentioned corotation takes place with the annular frame 16,the positions of the annular frames 15 and 16 located opposite eachother change, possibly damaging the moving floor 17 due to torsionalforce and preventing the level portion of the moving floor 17 from beingformed under the ring guide portion 16A. The medical particleirradiation apparatus 40 equipped with the anti-corotation mechanism 34does not present such a problem.

Since the connecting shaft 36 is supported by the inner surface of therotary shell 3 via a pair of the bearings 35, the anti-corotationmechanism 34 is moved in the rotation direction of the rotary shell 3 insynchronization with the rotation of the rotary shell 3 and the positionof contact between the sprocket 38 and the annular frame 16, morespecifically, the position of contact between the sprocket 38 and theconveyor chain 28 disposed on the outer radial surface of the annularframe 16 moves in that rotation direction in succession when rotation ofthe annular frame 16 is prevented as mentioned earlier. Theanti-corotation mechanism 34 and the particle irradiation unit 4 move inthat rotation direction as the rotary shell 3 rotates while keeping thepreset distance between them constant in the circumferential directionof the rotary shell 3. In Patent Document 2, since the particleirradiation unit interferes with the locking rod as a result of movementof the rotating gantry, it is necessary to extend or retract the lockingrod. With this embodiment, movement of the particle irradiation unit 4is never hindered by the anti-corotation mechanism 34.

This embodiment eliminates the need for the drive motor described inPatent Document 1 which rotates the mobile ring rail in the directionopposite to the rotation direction of the radiation irradiation unit bythe same amount as the amount of rotation of the radiation irradiationunit and the drive unit exclusively for the anti-corotation mechanism,an equivalent of the motor-operated cylinder described in PatentDocument 2 which moves the locking rod. Moreover, the control unit forthe drive unit is not required. With this embodiment, it is possible toprevent the annular frame 16 from rotating together with the rotatinggantry 1 using simple configurations not requiring the drive unitexclusively for the anti-corotation mechanism such as disposition of apair of the sprockets 37 and 38 coupled with the connecting shaft 36 onthe rotating gantry 1 and disposition of the conveyor chains on theannular frames 15 and 16. This ensures simplified configurations of theirradiation room for particle beam therapy 55, eventually allowingsimplified configurations of the medical particle irradiation apparatus40.

This embodiment essentially adopts a structure in which rotation of theannular frame 16, disposed such that it can rotate relative to therotating gantry 1, is prevented by the member engaged with the fixedannular frame 15. Since the member restrains 360-degree movement of theparticle irradiation unit 4 in the circumferential direction of therotary shell 3 with this structure, this embodiment has adopted aconfiguration which allows the member to move in the rotation directionof the rotating gantry 1 together with the particle irradiation unit 4by installing that member on the rotary shell 3, that is, the rotatinggantry 1.

The medical particle irradiation apparatus according to anotherembodiment of the present invention is described with reference to FIGS.9, 10, 11 and 12. A medical particle irradiation apparatus 40A of thisembodiment has configurations in which the irradiation room for particlebeam therapy 55 of the medical particle irradiation apparatus 40 in theembodiment is replaced with an irradiation room for particle beamtherapy 55A. Of the configurations of the irradiation room for particlebeam therapy 55A, those which are the same as the configurations of theirradiation room for particle beam therapy 55 are assigned the identicalsigns. The portions which are different from the configurations of theirradiation room for particle beam therapy 55 are described.

With the irradiation room for particle beam therapy 55A, a cylindricalchain attachment portion 16Aa is attached to the outer radial surface ofthe ring guide portion 16A with a bolt 40 (FIGS. 11 and 12). Theconveyor chain 28 is attached to the inner radial surface of the chainattachment portion 16Aa. Attachment of the conveyor chain 28 to thatinner radial surface is conducted using the bracket portion 31 as withthe irradiation room for particle beam therapy 55. The conveyor chain 28is attached to the ring guide portion 15A by attaching the conveyorchain 28 to the inner radial surface of a cylindrical chain attachmentportion 15Aa provided on the outer radial surface of the ring guideportion 15A as with the ring guide portion 16A.

The anti-corotation mechanism 34 has a pair of the sprockets 37 and 38coupled with the connecting shaft 36 and is provided on the inside ofthe rotary shell 3 (more specifically, the connecting shaft 36 issupported by a pair of the bearings 35, which are secured to theparticle irradiation unit 4, such that it is free to rotate (rotate onits axis) as shown in FIG. 10). The sprocket 37 of the anti-corotationmechanism 34 meshes with the conveyor chain 28 of the chain attachmentportion 15Aa while the sprocket 38 with the conveyor chain 28 of thechain attachment portion 16Aa. A center of rotation m′ of the connectingshaft 36 (axis of the sprocket 37 or 38) is substantially parallel withthe center of rotation k of the rotary shell 3 (=axis of the fixed frame15 or the rotary frame 16). That is, the distance from the axis of thesprocket 37 to the axis of the annular frame 15 is equal to the distancefrom the axis of the sprocket 38 to the axis of the annular frame 16.

Since the sprockets 37 and 38 also mesh with the corresponding conveyorchains 28 in this embodiment, the anti-corotation mechanism 34 moves inthe same direction as the rotation direction of the rotating gantry 1while rotating on its axis as the rotating gantry 1 rotates. Therefore,this embodiment also provides the same functions and effect offered bythe embodiment. Further, since the sprockets 37 and 38 mesh with theconveyor chains 28, provided on the respective inner radial surfaces ofthe chain attachment portions 15Aa and 16Aa, from inside the conveyorchains 28 in this embodiment, the outer diameters of the ring guideportions 15A and 16A can be made larger than those in the embodiment.Since the guide grooves 56 formed respectively on the ring guideportions 15A and 16A can be expanded outwardly, the moving floor 17meshes with the ring guide portions 15A and 16A at positions which arespread more outwardly than in the embodiment. This makes it possible toenlarge the therapy gauge 14 in the direction of the radius of therotary shell 3, thus allowing expansion of the therapy gauge 14 space.

With this embodiment, one of the conveyor chains 28 is indirectlyattached to the annular frame 15 via the chain attachment portion 15Aaand the ring guide portion 15A while the other conveyor chain 28 to theannular frame 16 via the chain attachment portion 16Aa and the ringguide portion 16A. However, attachment of the conveyor chains to theannular frames 15 and 16 may be conducted as described below. That is,the guide grooves 56 are formed on the respective side surfaces of theannular frames 15 and 16, and circular grooves wide enough toaccommodate the sprockets 37 and 38 are formed more outwardly than thoseguide grooves 56. The conveyor chains 28 are attached directly to theinner radial surfaces of those circular grooves which face the axis ofthe rotary shell 3. The sprockets 37 and 38 are slid into theirrespective circular grooves and made to mesh with the correspondingconveyor chains 28 from inside the conveyor chains 28. This provides thesame effect as with this embodiment. Further, it may be possible toattach the cylindrical chain attachment portions to the respective outerradial surfaces of the annular frames 15 and 16 on which the guidegrooves are formed and then attach the conveyor chains 28 to the innerradial surfaces of these chain attachment portions. It can be said thateach of the configurations discussed above substantially allows meshingof the annular frames 15 and 16 with the sprockets of theanti-corotation mechanism 34 outwardly from the rotation center of therotating gantry 1.

The sprockets provided on the anti-corotation mechanism mesh with theconveyor chains in each of the embodiments discussed above; however, thepresent invention is not limited to these embodiments and it may bepossible to employ a mesh contact configuration by gears or presscontact configuration in which they are engaged with one another byfrictional force resulting from the rollers' pressing force. Both ofthem provide the same effect.

Note that although the synchrotron 43 is employed in the aboveembodiments as ion beam acceleration means, a cyclotron may be usedinstead. If a cyclotron is used, the preaccelerator 42 is not requiredand the ion beam emitted from the ion source is introduced into thecyclotron, accelerated by the cyclotron and then emitted to the beamtransfer system 49. Further, the ion beam goes through the beam transferunit 5, after which the patient 8 on the therapy bed 59 is irradiatedwith the ion beam from the particle irradiation unit 4.

The present invention allows formation of the substantially level accessfloor by the flexible moving floor regardless of the position of theirradiation unit emitting particle beams. Further, the present inventionallows simplification of the apparatus configurations.

While illustrative and presently preferred embodiments of the presentinvention have been described in detail herein, it is to be understoodthat the inventive concepts may be otherwise variously embodied andemployed and that the appended claims are intended to be construed toinclude such variations except insofar as limited by the prior art.

What is claimed is:
 1. A medical particle irradiation apparatuscomprising: a rotating gantry including an irradiation unit emittingparticle beams; a first frame located within and supported by saidrotating gantry such that it can rotate relative to said rotatinggantry; a second frame fixedly located opposite said first frame; ananti-corotation unit disposed on said rotating gantry, saidanti-corotation unit being in contact with both said first and secondframes to prevent said first frame from rotating together with saidrotating gantry during rotation of said rotating gantry; and a flexiblemoving floor located between said first and second frames, said flexiblemoving floor being engaged with said first and second frames in such amanner as to move freely such that its bottom is substantially level andthat it moves as said rotating gantry rotates, wherein saidanti-corotation unit comprises a first rotational element having anuneven portion which meshes with a first uneven portion formed on saidfirst frame, a second rotational element having an uneven portion whichmeshes with a second uneven portion formed on said second frame, and ashaft member which couples said first and second rotational elementstogether, wherein said shaft member is attached to said rotating gantrysuch that said shaft member is free to rotate on its axis.
 2. Themedical particle irradiation apparatus according to claim 1, whereinsaid first and second frames are each provided with a moving floor guideunit engaged separately with both ends of said moving floor, said movingfloor guide unit having a level portion at the bottom.
 3. The medicalparticle irradiation apparatus according to claim 1, wherein said firstrotational element is in mesh with said first frame outwardly from thecenter of rotation of said rotating gantry, and said second rotationalelement is in mesh with said second frame outwardly from the center ofrotation of said rotating gantry.
 4. The medical particle irradiationapparatus according to claim 1, wherein said first rotational element isin mesh with said first frame toward the center of rotation of saidrotating gantry from the outside thereof, and said second rotationalelement is in mesh with said second frame toward the center of rotationof said rotating gantry from the outside thereof.
 5. A medical particleirradiation apparatus comprising: a rotating gantry including anirradiation unit emitting particle beams; a first frame located withinand supported by said rotating gantry such that it can rotate relativeto said rotating gantry; a second frame fixedly located opposite saidfirst frame; an anti-corotation unit disposed on said rotating gantry,said anti-corotation unit being in contact with both said first andsecond frames to keep the positions of said first and second frames,located opposite each other, substantially unchanged regardless of therotation of said rotating gantry; and a flexible moving floor locatedbetween said first and second frames, said flexible moving floor beingengaged with said first and second frames in such a manner as to movefreely such that its bottom is substantially level, that it formstherein a therapy room into which a therapy bed is slid and that itmoves as said rotating gantry rotates, wherein said anti-corotation unitcomprises a first rotational element having an uneven portion whichmeshes with a first uneven portion formed on said first frame, a secondrotational element having an uneven portion which meshes with a seconduneven portion formed on said second frame, and a shaft member whichcouples said first and second rotational elements together, wherein saidshaft member is attached to said rotating gantry such that said shaftmember is free to rotate on its axis.
 6. The medical particleirradiation apparatus according to claim 5, wherein said first andsecond frames are each provided with a moving floor guide unit engagedseparately with both ends of said moving floor, said moving floor guideunit having a level portion at the bottom.
 7. The medical particleirradiation apparatus according to claim 5, wherein said firstrotational element is in mesh with said first frame outwardly from thecenter of rotation of said rotating gantry, and said second rotationalelement is in mesh with said second frame outwardly from the center ofrotation of said rotating gantry.
 8. The medical particle irradiationapparatus according to claim 5, wherein said first rotational element isin mesh with said first frame toward the center of rotation of saidrotating gantry from the outside thereof, and said second rotationalelement is in mesh with said second frame toward the center of rotationof said rotating gantry from the outside thereof.
 9. A medical particleirradiation apparatus comprising: a rotating gantry including anirradiation unit emitting particle beams; a first frame located withinand supported by said rotating gantry such that it can rotate relativeto said rotating gantry; a second frame fixedly located opposite saidfirst frame; a frame position retaining unit disposed on said rotatinggantry and being in contact with both said first and second frames, saidframe position retaining unit moving in the circumferential direction ofsaid second frame as said rotating gantry rotates; and a flexible movingfloor located between said first and second frames, said flexible movingfloor being engaged with said first and second frames in such a manneras to move freely such that its bottom is substantially level, that itforms therein a therapy room into which a therapy bed is slid and thatit moves as said rotating gantry rotates, wherein said frame positionretaining unit comprises a first rotational element having an unevenportion which meshes with a first uneven portion formed on said firstframe, a second rotational element having an uneven portion which mesheswith a second uneven portion formed on said second frame, and a shaftmember which couples said first and second rotational elements together,wherein said shaft member is attached to said rotating gantry such thatsaid shaft member is free to rotate on its axis.